Pressure cylinder

ABSTRACT

A pressure cylinder which is formed from two sections which are joined together to enclose a volume which is bounded by two spaced walls with a settable filler between the walls.

BACKGROUND OF THE INVENTION

This invention relates to a pressure cylinder which can be used as awater heater or geyser for producing hot water for a domestic,industrial or other application, or as a gas container (cylinder) or inany other appropriate application which requires containment of apressurised fluid (liquid or gas).

A typical geyser or hot water tank is essentially a pressure vesselalthough, in order to avoid undue forces being exerted inside the vesselby water pressure, during use, it is known to make use of apressure-reducing valve at an inlet connection to the tank. Nonethelessthis type of vessel must be capable of withstanding a fair degree ofinternal pressure.

It is known to fabricate an inner tank of a geyser from rolled orpressed copper sheeting or steel which is welded or otherwise sealed sothat it is waterproof. Inlets and outlets are attached to the inner tankwhich thereafter is covered by an insulating material which, in turn, isencased in an outer protective skin e.g. of a light gauge metal.

The fabrication of a geyser of the aforementioned kind is time consumingand laborious and requires a fair degree of technical skill. Anotheradverse factor is that although metallic components of the geyser areprotected against corrosion they do have a limited life expectancy. Theuse of copper is expensive and generally has been discontinued.

Similar considerations apply in respect of containers for use with apressurised gas, for example liquid petroleum gas, propane, butane,natural gas etc.

The invention is concerned with a pressurised cylinder which can bemanufactured to a consistently high standard using a process which lendsitself to automation and which is inherently resistant to corrosive orfluid (liquid or gas) leakage effects.

SUMMARY OF THE INVENTION

The invention provides a pressure cylinder which includes a body whichis formed from at least two sections, each section including anintegrally formed inner wall and an outer wall which is spaced from theinner wall, and wherein the two sections are interconnected so that theinner walls enclose a fluid-containing volume inside the body.

“Fluid” as used herein includes a liquid and a gas.

Filler material may be located in a gap between the inner wall and theouter wall.

The filler material may be of any appropriate kind and preferably is arigid foam or similar settable material which may be injected into thegap to fill a void which is defined between opposing surfaces of theinner and outer walls and which bonds to these surfaces. For awater-heating application the filler material should have a good thermalinsulating characteristic. The filler material acts to transfer pressurebetween the inner and outer walls and subsequently rigidifies the bodydue to the resultant “sandwich-type” construction.

The inner wall may be of any appropriate shape and preferably includes asubstantially cylindrical portion and an end piece at a first end of thecylindrical portion. The end piece is preferably domed so that itscapability of withstanding force exerted by fluid pressure in the volumeis increased.

The outer wall is preferably substantially cylindrical.

The section is preferably made in a moulding process and, to facilitatethe moulding operation, the cylindrical inner wall portion and thecylindrical outer wall portion may be slightly tapered to enable thesection to be released from a mould.

The inner wall, at a second end which is remote from the first end, maybe attached to the outer wall by means of an annular component whichacts as a bridge between the inner and outer walls. The annularcomponent may lie in a plane which is substantially at a right angle toa longitudinal axis of the body.

The outer wall, on an external surface, may be formed with a recesswhich extends circumferentially around the outer wall adjacent theannular component.

The end piece of the inner wall may be formed with at least one inlet oroutlet aperture. Preferably such aperture is in the form of a spigotwhich projects from an outer surface of the end piece e.g. in adirection which is substantially parallel to a longitudinal axis of thebody.

Each spigot may be threaded to enable a screw coupling to be made to it.The spigot may be reinforced at a junction between the spigot and theend piece, for example by means of one or more webs or enlargedsections. The spigot or aperture may be provided with a metal or plasticinsert which can be moulded into, or otherwise attached to, the section.

The two sections may be substantially identical.

The two sections may be interconnected in any appropriate way, forexample by joining the annular components to each other. This may bedone using any suitable mechanism or process. For example use may bemade of an adhesive or, preferably, the sections are joined by frictionor heat welding abutting and opposing surfaces of the annular componentsto each other.

A ring or band may extend around the body and may be positioned in therecesses in the outer walls which are side-by-side once the sections areinterconnected. The band may be provided for reinforcing or aesthetic orfor both purposes.

Each section may be made from any appropriate material such as PET orpolyamide or polyolefin with performance enhancers. Such materials areknown in the art. If the cylinder is to be used for containing gas, thematerial used must be resistant to gas permeation.

In order to enhance the rigidity of the body at least one section may beformed with ribs or other formations which extend into the gap betweenthe inner wall and the outer wall. These formations are preferablyaligned with a longitudinal axis of each section to facilitatefabrication thereof during a moulding process. The formations areintegrally formed with at least one of the walls.

The pressure cylinder may include at least one end cap and preferablytwo end caps. Each end cap is engaged with a respective end of the body.Each end cap may be secured to the body by means of formations whichengage with complementary formations in the respective sections e.g. inthe inner wall or in the outer wall or both.

The end cap is preferably formed with apertures through which thespigots in the associated end wall extend, preferably with a close fitwhich nonetheless permits a degree of relative movement, due for exampleto thermal effects which result in expansion or contraction, between thesection and the end cap. The number of apertures may vary according tothe intended application, for example for gas a single nozzle isprovided for filling and dispensing, and for water (i.e. the cylinder isused as a geyser) multiple appropriate apertures are provided.

Each end cap may be flat, domed or include formations which providestable support for the body if the body is positioned in a verticalorientation i.e. with a longitudinal axis of the body extendingvertically. Similarly each end cap or the outer wall of each section, orboth, may include formations which provide stable support for the bodywhen it is horizontally orientated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference tothe accompanying drawings in which:

FIG. 1 is a perspective view of a pressure cylinder according to theinvention in an exploded configuration,

FIG. 2 is a perspective view of the pressure cylinder of FIG. 1 fullyassembled,

FIG. 3 is a side view of the pressure cylinder,

FIG. 4 shows, in cross section, on an enlarged scale, a section which isused with a similar section to make a body of the pressure cylinder,

FIG. 5 shows the pressure cylinder in cross section,

FIG. 6 is a plan view of an end cap used in the pressure cylinder,

FIG. 7 is a side view of the end cap, and

FIG. 8 illustrates a possible variation to the end cap.

DESCRIPTION OF PREFERRED EMBODIMENT

FIGS. 1 and 2 of the accompanying drawings are perspective views of apressure cylinder 10 according to the invention in an explodedconfiguration and in a fully assembled mode, respectively. FIG. 3 is aside view of the pressure cylinder.

The pressure cylinder includes a body 12 and end caps 14 and 16. Thebody, in turn, consists of two sections 18 and 19 respectively which aresubstantially identical. FIG. 4 illustrates the section 18 in crosssection and on an enlarged scale.

The following description relates to the section 18. It is to beunderstood however that the section 19 is for all practical purposes thesame as the section 18.

The section 18 includes an inner wall 20 with an end piece 22 and anouter wall 24. An annular component 26 lies in a plane 28 which is at aright angle to a longitudinal axis 30 of the section. The component isintegrally formed with the inner and outer walls and acts as a bridgingmember which interconnects a first end 32 of the inner wall to anadjacent first end 34 of the outer wall. The outer wall is taperedslightly towards the end piece. At a junction with the annular componentthe outer wall has a circumferentially extending recessed formation 36.

The inner wall 20 has a mouth 38 at the first end which opposes the endpiece. Between the mouth and the end piece the inner wall is taperedslightly inwardly towards the end piece.

The end piece 22, which is integrally formed with the inner wall 20, isdomed. As illustrated the pressure cylinder is intended to be used as awater heater (geyser) and for this application, which is exemplary only,a number of spigots 40 are integrally formed with the end piece andproject in an axial direction, i.e. substantially parallel to thelongitudinal axis 30, from the end piece. If the cylinder is to be usedas a gas cylinder then a single spigot or moulded-in nozzle (not shown)would be formed to act as a filling and dispensing aperture, in place ofthe spigots 40.

The spigots are externally or internally threaded, to standard threadgauges, according to requirement. To achieve this in a cost-effectiveand robust manner each spigot may be formed by means of a moulded-inmetal insert. Each spigot is tubular and projects from a correspondingaperture 42 formed through the end piece. Each spigot can be stiffenedor reinforced by means of a rib or web 44 which is formed between a baseof the spigot and an adjacent surface of the end piece.

A small double rim 46 on an outer surface of the end piece extends alonga circular path around the spigots.

The outer wall 24 is formed with a number of holes 50 at spacedlocations opposing the end piece 22—see FIG. 1.

The section 18 is formed in a suitable moulding process. The taper onthe inner wall 30 facilitates release of the section from a suitabletool, not shown. Similarly the spigots are aligned with the longitudinalaxis 30 so that such spigots can be integrally formed with the endpiece.

It is also possible during the moulding process, to form ribs or otherreinforcing formations, not shown, in a substantially cylindricalannular gap 52 between opposing surfaces of the inner and outer walls.

The end caps 14 and 16 are also substantially identical. Each end caphas a substantially circular, slightly domed, cover 60, see FIG. 6, withfour projecting feet 62, 64, 66 and 68 respectively which are spacedfrom each other and which impart a castellated appearance to the endcap. Apertures 70 are formed in a circular central section 72 of eachend cap, at spaced locations from each other, corresponding to theposition and shape of the respective spigots. The section 72 issurrounded by a circular wall 73—see FIGS. 1 and 7.

Flexible lugs 74 with hook-shaped formations 76 at their extremitiesextend from an outer rim 78 of the cover 60—see FIG. 7. Alternativelythe hook-shaped lugs can be on an inner wall surface of the end cap,allowing the end cap to fit over the holes 50.

Alternatively, as is shown in FIG. 8, a central circular section 72A (ofa modified end cap 14A) is substantially flat, with a central aperture70A. This would be an appropriate construction for a gas cylinder. Thehook-shaped lugs are dispensed with for the cap 14A is attached to abody section by passing suitable fasteners (not shown) through holes 79in a rim 78A of the cover which are brought into register with therespective holes 50 in the body section.

The end caps are manufactured in a suitable moulding process. Thevarious formations on each end cap are positioned to facilitatefabrication thereof in a direct manner without resorting to complexmoulding techniques.

The body sections 18 and 19, which for practical purposes are identical,are moulded independently of each other. Use is made of any appropriateplastics material such as a polyamide or polyolefin or PET with suitableenhancers. These materials are suitable for a water-heating applicationbut, for a gas-containment application, might require modification orreplacement to ensure that the sections are resistant to gas permeation.The thickness of the inner wall and of the outer wall can be variedaccording to requirement and structural characteristics, but typicallylies in the range of from 4 mm to 6 mm.

When each end cap 14, 16 is clipped into position, the apertures 70 ineach cover are aligned with the corresponding spigots 40 and the coversare then pushed home so that the hook-shaped lugs are deflected and canthen engage with a spring action with the holes 50 in the outer wall 24.

The cover is located in position not only by the hook-shaped lugs butalso by means of the rim 46 which engages with the wall 73 on the innersurface of the cover.

Optional fixing holes 82 are provided in the cover for fasteners whichare used to fix the cover mechanically to the corresponding bodysection.

A rigid foam material 84 is injected into the annular gap 52 of eachsection—see FIG. 5. This can be done before the end caps are fixed inposition but preferably is done after the end caps are fixed inposition. The foam completely fills the void and to a substantial extentis bonded in position. The bonding action can be enhanced by formingkeying formations in the surfaces of the inner and outer walls whichface into the gap 52. The foam substantially rigidifies the walls andimparts hoop strength to the section. As each end piece 22 is domedoutwardly it is inherently capable of withstanding substantial fluidpressure which arises in the volume inside the body. This capability ishowever enhanced by the use of the foam, if it is used. The foam, in awater-heating application, must have a good thermal insulatingcharacteristic, a factor which is of lesser importance in a gascontainment application.

Each domed end piece can be reinforced, as necessary, by moulding anetwork of honeycombed or radial ribs 46A on an outer surface 22Aintegrally with the end piece. These ribs, shown in dotted outline onlyin FIG. 4, typically would extend over the surface 22A and for examplemerge and terminate with various webs 44 adjacent the spigots 40. Thespigots, in themselves, extend in the axial direction of the body andthus also inherently act to stiffen the domed end piece.

The two sections 18 and 19 are joined to each other by means of a heator other welding process which bonds the outer surfaces of the annularcomponents 26 to each other. Thereafter a band 86 is placed around theouter walls, located in the abutting recesses 36. The band provides anaesthetic function in that it covers the joint line between the twosections but also acts to some extent as a reinforcing component for itincreases the hoop strength of the body 12 at a central location of thebody.

Each spigot passes with a tight fit through the corresponding aperturebut in a manner which allows for a limited degree of relative movementto take place between the body section and each end cap arising, forexample, from thermal expansive or contractive actions. The tight fitalso reduces the likelihood of fluid, from any source, passing throughthe interface between the cover and the spigot and then entering therigidifying foam inside the gap 52.

The number of spigots in each end piece varies according to requirement.Typically, if the cylinder is to be used as a geyser, provision is madefor a cold water inlet, a hot water outlet, the mounting of an electricelement, the mounting of a control thermostat, a pressure or thermalrelease valve and an outlet for water drainage.

The pressure cylinder of the invention offers a number of advantages. Itis made from two halves which are welded together to provide a smoothexternal cylindrical appearance. Reinforcement features and otherconstructional formations are hidden from external view. The cylinderthus has a smooth, aesthetically pleasing, appearance. Of significanceis the fact that the annular components 26 constitute flanges, which maybe about 50 mm wide, which are radially aligned relatively to thecentral axis 30. These flanges are bonded together in the assemblyprocess and, inherently, provide reinforcing at the centre of the body.The flanges, in turn, are stiffened by the inner and outer side wallsand the intervening foam material which act, collectively, to brace theflanges against deflection in a sideways direction i.e. in a directionwhich is lateral to the width of each flange. This allows the resultingbody, which is formed from components made by conventional injectionmoulding techniques, to withstand the high forces which are generated byfluid (water or gas) pressure inside the body.

The threaded spigots are integrally moulded in the end pieces optionallyusing pre-formed inserts. The likelihood of leakages occurring between aseparately formed spigot and an end piece to which the spigot isattached, as is the case in prior art pressure cylinders, is thuseliminated.

The end caps close off the foam material in the gap 52, and theprojecting feet 68 to a substantial extent protect pipe connectionswhich are made to these spigots. On the other hand, access to thespigots is permitted inter alia by means of the gaps between adjacentfeet.

The feet 62 to 68 can be used to support the body 12 in a verticalorientation, if required. If the cylinder is to be used in a horizontalorientation the shape of the feet can be altered to provide a stable,ground-engaging support. Another possibility is to form appropriateformations on the outer walls of the body sections so that the body canbe supported horizontally, when required. It is also possible to attacha respective band to the outer wall of each body section and for theband to carry ground-engaging members with flat surfaces which stabilisethe cylinder when it is placed on a horizontal surface.

The rigid foam between the inner and outer walls creates a beam effectwhich distributes forces which arise from internal pressure in thevolume inside the body, during use.

As the body is made from a thermoplastic material it is inert andcorrosion resistant and thus has substantial life expectancy.

1. A pressure cylinder which includes a body which is formed from at least two sections, each section including an integrally formed inner wall and an outer wall which is spaced from the inner wall, and wherein the two sections are interconnected so that the inner walls enclose a fluid-containing volume inside the body.
 2. A pressure cylinder according to claim 1 wherein a settable material is located in a void between opposing surfaces of the inner and outer walls and is bonded to these surfaces.
 3. A pressure cylinder according to claim 1 wherein, for each section, the inner wall has a substantially cylindrical portion which is tapered and an end piece at a first end of the cylindrical portion which is domed, and the outer wall is substantially cylindrical and is tapered.
 4. A pressure cylinder according to claim 3 wherein the inner wall, at a second end which is remote from the first end, is attached to the outer wall by means of an annular component which acts as a bridge between the inner and outer walls and which lies in a plane which is substantially at a right angle to a longitudinal axis of the body.
 5. A pressure cylinder according to claim 4 wherein the outer wall, on an external surface, is formed with a recess which extends circumferentially around the outer wall adjacent the annular component.
 6. A pressure cylinder according to claim 3 wherein the end piece of the inner wall is formed with at least one inlet or outlet aperture.
 7. A pressure cylinder according to claim 6 wherein the aperture is in the form of a spigot which projects from an outer surface of the end piece in a direction which is substantially parallel to a longitudinal axis of the body and which is threaded to enable a screw coupling to be made to it.
 8. A pressure cylinder according to claim 5 wherein the two sections are substantially identical and are interconnected by joining the annular components to each other and wherein a reinforcing band, which is positioned in the recesses in the outer walls, extends around the body.
 9. A pressure cylinder according to claim 1 wherein each section has formations which are integrally formed with at least one of the walls and which extend into the gap between the inner wall and the outer wall.
 10. A pressure cylinder according to claim 1 which includes two end caps, and wherein each end cap is engaged with a respective end of the body and is secured to the body by means of formations which engage with complementary formations in the respective sections. 